LinuxQuestions.org - Mount virtualbox hardisk to ramdisk problem

I search online and read some post saying that seemingly a user can mount virtualbox disk to ramdisk so that i/o can be speed up. However, when trying to mount vdi to ramdisk, I encounter some problems.

I create a virtualbox server as normal steps.

Then I create a dir and mount it as ramdisk with following command

Code:

mount -t tmpfs -o size=1G /path/to/vbox/server

However, when starting the server it throws error

Code:

Runtime error opening '~/VirtualBox VMs/server/server.vbox' for reading: -102 (File not found.).

/build/buildd-virtualbox_4.1.4-dfsg-1-i386-f9UKjT/virtualbox-4.1.4-dfsg/src/VBox/Main/src-server/MachineImpl.cpp[685] (nsresult Machine::registeredInit()).

Result Code: 

NS_ERROR_FAILURE (0x80004005)

Component: 

VirtualBox

Interface: 

IVirtualBox {c28be65f-1a8f-43b4-81f1-eb60cb516e66}

After googling I can not find threads discussing how to do that. Or similar error being solved. What keyword should I use? Or what is the correct step to mount vbox disk to ramdisk for speeding up i/o?

Thanks